Bithyniid snails as hosts of Opisthorchiidae and Notocotylidae in the south of Western Siberia, Russia.

Opisthorchiasis and related infections are persistent and substantial public health burdens from eastern Europe to southeastern and northern Asia. Snails of the family Bithyniidae act as first intermediate hosts not only for the trematodes of the family Opisthorchiidae but also for those of the family Notocotylidae. There are certain morphological similarities between the aforementioned trematode cercariae. In order to find natural local foci of opisthorchiasis, which are established primarily according to the presence of infected bithyniid snails at the area under examination, it is crucial to correctly identify the rediae and cercariae of the trematodes. The aim of our investigation was to evaluate the role of bithyniid snails in the transmission of Opisthorchiidae and Notocotylidae in ecosystems in the south of Western Siberia. We have been studying the process of bithyniid snail dissemination in Western Siberia and examining their infection by trematodes from 1994 until now. A total of 16,213 bithyniid snails in 23 water bodies (in 28 localities) of four major basins situated in the Novosibirsk region were inspected for trematode infestation. Long-term research has been conducted in the Kargat river estuary and the Ob river floodplain for 15 and 25 years, respectively. In both water bodies, the prevalence of notocotylid and opisthorchiid trematodes was positively correlated with the global land-ocean temperature index. Trematode parthenitae were identified if there were mature cercariae capable of leaving the shell of the host snail on their own. Identification to the species of opisthorchiid cercariae was verified using molecular genetic analysis methods targeting ITS2 locus. Opisthorchis felineus and Metorchis bilis, two opisthorchiid species that are potentially perilous to human health, were found in bithyniids in the Novosibirsk region. The mean prevalence of infection with notocotylid trematodes in bithyniid snails was higher than the corresponding prevalence of infection with opisthorchiid trematodes. The results of this study can be used to identify and predict natural foci of epidemiologically and/or epizootically dangerous diseases.

The influence of trematode metacercariae on the individual fecundity of Bithynia troscheli (Gastropnoda: Bithyniidlae).

Fifteen trematode species belonging to seven families parasitizing the females of Bithynia troscheli (Paasch, 1842) at metacercarial stage, were recorded in Kargat River (Lake Chany, South of West Siberia, Russia). The breeding mollusk females have less metacercarial diversity (9 species vs. 15) and lower mean parasite abundance, comparing to non-ovigerous mollusks. The hypothesis of the metacercarial influence on individual fecundity of aquatic gastropods was tested. The individual fecundit pariameters of the-B. troscheli females, uninfected and infected with the trematode metacercariae belonging to fam. Echinostomatidae, Cyathocotilidae, Strigeidae, Cyclocoelidae, were compared. The percentage of the breeding B. troscheli females--was less and their fecundity parameters were lower for the hosts infected (with the Strigeidae or Cyclocoelidae metacercariae) comparing to non-infected ones. Trematode metacercariae found in the mantle or somatic musculature had no significant effects on the fecundity of the host. However, our results showed that trematode metacercariae affect the reproduction of B. troscheli in dual ways. All fecundity parameters of the mollusk females with the high infection rate were, significantly lower than those for uninfected females: the percentage of fecund females (chi2 = 6.73 ,p < 0.01), number of clutches per female, number of egg capsules per clutch and number of normal egg capsules per female (Tukey HSD, p < 0.001). Although the females with-low intensity of metacercarial infection lay egg clutches significantly more frequently than uninfected ones (chi2 = = 4.18, P = 0.04); the fecundity parameters were approximately equal for both groups of the mollusk females. These pioneer results prove the reality of influence of metacercariae on the individual fecundity of aquatic gastropods. The regulatory population mechanisms that may compensate the host reproduction loss caused by metacercaria, are discussed.

[Characteristics of the seasonal development of Schistogonimus rarus (Trematoda: Prosthogonimidae). An essay on quantitative estimation of the trematode in the ecosystem of the Malye Chany lake (south of Western Siberia)].

Quantitative estimation of the trematode Schistogonimus rarus at the stage of cercaria is carried out in the ecosystem of the Malye Chany lake, south of Western Siberia, on the base of long-term data obtained in 1995-2002. Average daily emission of the S. rarus cercaria was shown to be significantly higher in larger mollusc hosts (p < 0.01), by the results of laboratory investigations. Moreover, significant decrease of the average daily emission of the S. rarus cercaria from June to July is established (p < 0.01). It was revealed, that emission of the S. rarus cercaria in the south of Western Siberia (both in natural and laboratory conditions) lasts no more than 50 days and is finished in August. The infestation rate of the mollusc host Bithynia troschelii by the S. rarus parthenites varied from 0.28 to 1.44 % in different years and correlated with the water temperature at first ten days of June (r = 0.75). Flow of the S. rarus cercaria (specimens per square meter) was estimated on the base of the quantitative characteristics of the cercaria emission, data on the infestation rate of the host population, and data on the host abundance. The flow of the cercaria varied from 6000 (in 1998) up to 330000 (in 2000) per season and correlated with the water temperature in third ten days of June (r = 0.71).

The spatial relationship between the musculature and the NADPH-diaphorase activity, 5-HT and FMRFamide immunoreactivities in redia, cercaria and adult Echinoparyphium aconiatum (Digenea).

The spatial relationship between the musculature and the NADPH-diaphorase (NADPH-d) activity, 5-HT and FMRFamide immunoreactivities in redia, cercaria and adult Echinoparyphium aconiatum was studied using scanning electron microscopy (SEM), NADPH-d histochemistry, immunocytochemistry, and confocal scanning laser microscopy (CSLM). TRITC-conjugated phalloidin was used to stain the musculature. Staining for NADPH-d was observed in the central (CNS) and peripheral nervous system (PNS) of all three stages. NADPH-d positive nerves occurred very close to muscle fibres. 5-HT-immunoreactive (5-HT-IR) nerve cells and fibres occurred in the CNS and PNS and close to muscle fibres. FMRFamide-IR nerve fibres were observed in the CNS and PNS of adult worms. This is the first time, the presence of the NADPH-d has been demonstrated in the larval as well as the adult stages of a fluke.

[Distribution of trematodes of the family Prosthogonimidae in river and lake ecological systems in the south of the Western Siberia].

The results of long-term investigations (1994-2003) of an infection rate of trematodes of the family Prosthogonimidae in the first intermediate hosts (snails of the family Bithyniidae) and in the final hosts (birds) from a basin of the Chany Lake (Western Siberia) are discussed. A total of 1824 specimens of Bithynia tentaculata (L., 1758) and 7166 specimens of Opisthorchophorus troscheli (Paasch, 1842) have been collected from eight rivers and two lakes in the south of the Western Siberia. Data of incomplete helminthological dissection of 225 young water-fowl of 18 species were analyzed. Birds were obtained in July, August and September, 1996-2003 from the Chany lake basin. Maritas of the trematode family Prosthogonimidae were revealed in bursa Fabricii (26.12%) of seven bird species of two orders (Anseriformes and Gruiformes): Grey Lag-Goose Anser anser (L.) (Infection rate-28.6% +/- 12.1), Mallard Anas platyrhynchos L. (27.5% +/- 6.2), Shoveler--A. clypeata L. (22.2% +/- 13.9), Pochard Aythya ferina (L.) (51.7% +/- 9.3), Coot Fulica atra L. (28.6% +/- 5.6), Tufted Duck A. fuligula (L.) (1 case), Wigeon A. penelope L. (1 case). Average intensity of invasion is 5.8 marita specimens per infected bird. The maximal number of parasites (37 maritas), and also the highest average intensity of invasion are recorded for the Coot. The 342 maritas of the family Prosthogonimidae belong to three species: Prosthogonimus ovatus (Rud., 1803) (49.7%), P. cuneatus (Rud., 1809) (32.8%) and Schistogonimus rarus (Braun, 1901) (14.6%); these trematode species have been recorded in 35, 12 and 8 bird species, respectively. Grey Lag-Goose, Shoveler, Pochard and Tufted Duck are new host records for P. cuneatus in for Western Siberia. Parthenitae of trematodes (Prosthogonimidae) were revealed from eight populations of bithyniid snails. The infection rate of the trematodes (parthenitae and cercariae) in population of bithyniid snails from lake ecological system varied 6.55-54.4%, and in river ecological systems in was 0.6-4.2 %. The infection rate of trematodes (parthenitae and cercariae) of the first intermediate hosts was 2.64% that is significantly lower than that of the final hosts from the Chany Lake basin. Both O. troscheli and B. tentaculata were noted as the first intermediate hosts of prosthogonimid trematodes of three species: P. ovatus, P. cuneatus and S. rarus. All three species of trematode were found in three water reservoirs: Ob River (B. tentaculata), Kargat River (O. troscheli) and Chany Lake (O. troscheli). Thus it is found out that 39 bird species can be the final hosts of prosthogonimid trematodes. About a quarter of nestlings is infected with these trematodes. The infection rate of parthenitae in snails from the lake ecosystems is significantly higher than in the river ecosystems.

[New data on Cyathocotyle bushiensis (Trematoda: Cyathocotylidae)]. / Novye svedeniia o Cyathocotyle bushiensis (Trematoda: Cyanocotylidae).

Metacercariae of Cyathocotyle bushiensis Khan, 1962 (Digenea) were found in populations of seven species of gastropod snails collected from lakes and rivers in the south of West Siberia (Russia). This is the first record of C. bushiensis in Russia. Five species of snails, Lymnaea stagnalis, L. palustris, L. tumida, Planorbis planorbis (Pulmonata) and Viviparus viviparus (Prosobranchia) were recorded as new hosts for the metacercariae of C. bushiensis. The infection rate of Bithynia tentaculata and Opisthorchophorus (= Codiella) troscheli (Prosobranchia), the main hosts of C. bushiensis metacercariae, was analyzed in regard to the sex and shell length of molluscs. It was revealed that infection rate and mean intensity of metacercariae increases with the shell lengths. Drawings and descriptions of excysted metacercariae from naturally infected snails and adult worms from experimentally infected domestic ducklings are given.